Hematein or hematoxylin-containing zinc oxide photoconductive layers

ABSTRACT

An electrophotographic layer composed of a zinc oxide photoconductor, a resinous binder and at least one compound selected from hematein and hematoxylin.

mfiefi States Patent [191 [111 3,725,%@ Taimoto et al. 1 Apr. 3, 1973 [54] HEMATEIN 0R HEMATOXYLIN- [56] References Cited CONTAINING ZINC OXIDE PHOTOCONDUCTIVE LAYERS UNTED STATES PATENTS 3,671,235 1972 Y [75] Invent: atzi z k zg ggl 3,682,631 251972 "32%.: 73 Assignee: Fuji Photo Film 00., um, 'f' y E 'flW Lesmes Kanagawa Japan Assistant Exammer-M. B. wlttenberg [22] Mr Sam 24 1971 Attorney-FergusonKc Baker 21] Appl. No.: 183,706 [571 ABSTRACT An electrophotographic. layer composed of a zinc oxide photoconductor, a resinous binder and at least CCll 86.52216; one compound selected from hematein and hematox 581 Field ofSearch ..96/1.5,1.7,1.8;252/50l ym 4 Claims, No Drawings HEMATEIN R HEMATOXYLIN-CONTAINING ZINC OXIDE PHOTOCONDUCTIVE LAYERS This invention is concerned with a remarkable improvement in continuous tone reproducibility of the photosensitive layer for electrophotography comprising zinc oxide and film formable resinous binder.

When the electrostatic development is employed, the reproduced image on the electrophotographic photosensitive layer has very hard tone which is inadequate of reproducing continuous tone image such as photographs of silver halide. Therefore, only letters, marks, figures and the so-called screened picture have been reproduced by using the usual layer.

The electrolytic electrophotography is known as an easy way to reproduce continuous tone image. It is conveniently employed to reproduce positive image from negative original while requires considerably complicated procedure in the case of positive to positive work. On the other hand, it is well known that the electrostatic development gives positive image from both negative and positive original by only changing the polarity of toners. Then inventors have studied on effective compounds toadd to the electrophotographic photosensitive layer in order that continuous tone image can be easily reproduced.

According to D. A. Ross, etc., Photographic Science and Engineering 13(5) 265-270 (1969), it is shown that addition of sensitizing dye to the electrophotographic photosensitive layer increases the sensitivity and at the same time improves the continuous tone reproducibility. This conclusion is in good agreement with the experimental results but not all the dyes show the same result.

It is predicted from this theory that the increment of amount of sensitizing dye improves continuous tone reproducibility together with the increase of sensitivity. Much amount of sensitizing dye for the improvement of the tone reproducibility causes coloring of photosensitive layer and increase of manufacturing cost. Then, the object of this invention is to prepare a special electrophotographic photosensitive layer by addition. of only small amount of compounds which can improve the continuous tone reproducibility.

The other object of this invention is finding the manufacturing process in which said compounds do not damage the required characteristics of the electrophotographic photosensitive layer.

Then the objects of this inventionare attained by adding at least one of the following compounds, hem atein and hematoxylin, to the electrophotographic photosensitive layer, comprising zinc oxide and film formable resinous binder.

Both hematein and hematoxylin are easily added to the layer in the same manner as that for the usual sensitizing dyes of zinc oxide. When we use the sensitizing dyes, we may regard these additives as one of the sensitizing dyes and may add them together with other dyes.

It is considered that both hematein and hematoxylin act on zinc oxide in the similar way. Each methanol solution of these additives has a red-brown color. Zinc oxide thrown into the solution adsorbs the additive on its surface and changes into light-violet color. So that usual zinc oxide is changed to the additive adsorbed one with light absorption range from 450 my. to 650 my. in wavelength.

Since hematein and hematoxylin in this invention is used in the same manner as that for many other dyes,

used several usually known methods can be employed; pouring the additive solution into the suspension after dispersing zinc oxide into the resinous binder, dispersing zinc oxide which has already adsorbed the additive on it into the resinous binder, or immersing the electrophotographic photosensitive layer into the additive solution after the layer has been dried. As mentioned above, it is possible to use the additive together with the sensitizing dye in the same solution.

Hematein or hematoxylin in this invention can be used in the range of 0.0001 5 2.0 parts by weight per parts by weight of zinc oxide. It is preferably to use them in the range of 0.0001 0.1 parts by weight for the electrostatic electrophotography, while for electrolytic electrophotography in range of 0.0001 1.0 parts by weight. In the above mentioned range the lower limit shows the minimum amount at that the effect of the additive is really recognized and the upper limit shows the maximum amount at that the deterioration of dark decay characteristics is permissible in the case of electrostatic electrophotography and in the case of electrolytic electrophotography the background density due to the dark current is negligible. Since these ranges are considerably affected by the combination of zinc oxide, sensitizing dye and film formable resinous binder, they cannot be explicitly determined.

All the dyes which have been known as the good sensitizer for zinc oxide can be used together with the additives in this invention. Xanthane-group, triphenylmethan-group, sulphonephthalein-group, cyaninegroup and merocyaninegroup dyes are especially effective. Specific dyes are described, for example, in U. S. Pat. No. 3,052,540.

All the known film formable resinous binders for zinc oxide can be employed in the invention. The typical binders are as follows: vinyl chloride-vinyl acetate copolymer, styrene-butadiene copolymer, styrene-butylmethacrylate copolymer, polyalkylmetacrylate, polyalkylacrylate, polyvinyl acetate, polyvinylbutylal, alkyd resin, silicon resin, epoxy resin, epoxi ester resin, etc. Another examples of good binder are those which can be cross-linked with polyisocyanate compound; copolymer of vinyl monomer with hydroxyl group which can react to isocyanate, and one or more monomers selected from styrene, alkylmetacrylate and alkylalkylate, alkyd and epoxyester. They are used with polyisocyanate compound and crosslinked.

The molecular formula of hematein is C, H, O and it is a kind of chroman compounds and has the following structure.

Hematoxylin is also a kind of chroman compounds. lts molecular formula is C H O and it has the following structure. They act as a pH indicator in the range of pH 5-6.

(|)H (IJH 0 O HO H 0 l l l l H 0 O H O O H hematein hematoxyl in When they are adsorbed on zinc oxide, violet color appears.

The details of this invention will be described in connection with the following examples.

Example 1 Methanol solution of 0.03 percent hematein and 0.03 percent brilliant blue FCF (Color lndex No. 42,090), were prepared respectively. 100 parts by weight of zinc oxide (Sazex 2000 supplied by Sakai Kagaku Ltd. and so on), 20 parts by weight of vinyl chloride-vinyl acetate copolymer (85:15) and 90 parts by weight of n-butyl acetate as the solvent were mixed in a ceramic ballmill, and the white suspension was obtained. This suspension was divided into three parts. One of them was applied on aluminum foil to make an electrophotographic photosensitive layer of about 10 p. thick on dry base. (Sample 1). The second was added by 10 parts by weight of hematein solution, per 100 parts by weight of zinc oxide while the last one by 10 parts by weight of brilliant FCF solution. They were stirred well with the homogenizer respectively and also applied on aluminum foil to make a layer of the similar thickness. (Sample 11, Ill). The electrophotographic characteristics of these samples are shown in Table 1.

TABLE 1 sample im/Vii E D 7 R 1 200 i 1.8 2.2 0.8 11 200 90% 7 1.6 1.2 1.3 111 Z0() 93% 5 1.3 1.5 1.2

Symbols used in Table l are as follows respectively, and will be used in the following examples.

V :lnitial voltage.

V Voltage after 60 second dark decay.

E :Relative value of exposure required for the half reduction of the initial voltage.

Difference between maximum density and minimum density in the case of developing the stepwedge pattern of D 0.15 by liquid developer. 7 An index of relation between exposure and image density obtained by the above mentioned development, i.e., a slope of two parallel lines which have clearance of D 0.10 and hold the characteristic curve between themselves. average gamma Reproducible logarithmic exposure range represented by DH.

Then this invention aims to make R value as large as possible where D value is not rendered so small. Example 1 shows that hematein is preferable in comparison with brilliant blue FCF, one of the effective sensitizing dyes.

Example 2 TABLE 11 Sample 1V Sample V Sample V1 fluorescein 0.003 parts 0.003 parts 0.003 parts by weight by weight by weight resebengal 0.003 0.002 0.001 brilliant blue FCF 0.003 0.003 0.003 hematoxylin 0 0.001 0.002 methanol 300 300 300 A hundred parts by weight of zinc oxide were respectively added into the methanol solutions shown in Table 11 and hematoxylin and/or dyes, were adsorbed. The adsorbed zinc oxide was dried in the dark place after centrifuging. We took 100 parts by weight of this zinc oxide into 24 parts by weight of 50 percent solution of styrene modified alkyd resin (styresol 4400 supplied by Nihon Reichhold Ltd.) together with 50 parts by weight of n-butyl acetate and 10 parts by weight of xylene as solvents. They were mixed and stirred in a ceramic ballmill during 16 hours. -To the obtained suspension was added 20 parts by weight of 40 percent solution of polyisocyanate compound (Desmodur L- supplied by Bayer Ltd.) to be hardened by cross-linking styrene modified alkyd resin and stirred. Then it was applied on aluminum foil to make a layer of about 10 11.. Thus we obtained Sample 1V, V and V1. The hardening of resinous binder was promoted by maintaining samples at 50C. during 20 hours after drying in the dark place.

TABLE 111 Sample V OW/ 0 E D R 1V 350V 88% 1.0 1.6 1.1 1.5 V "350 87 1.0 1.6 1.0 1.6 V1 -330 83 1.1 1.6 0.9 1.8

The electrophotographic characteristics are shown in Table 111. It is recognized that R value increases in accordance with the increment of hematoxylin.

Example 3 A hundred parts by weight of zinc oxide, 25 parts by weight of styrene-butadiene copolymer (85:15) and parts by weight of toluene as the solvent were mixed in a ceramic ballmill during 5 hours, and the white suspension was obtained. Ten parts by weight of hematein 0.1 percent methanol solution was added in the other ballmill and milling continued 5 hours, also.

They were applied on aluminum foil make a photosensitive layer of about 10 a and they were named Sample V11, V111 (containing hematein).

As a result of electrolytic development using 0.5 percent solution of triphenyltetrazoliumchloride, while gamma of V11 was 1.0 and V111 was 0.75, no difference between sample V11 and Vlll was found in D value (D=1.2). Comparing the exposure of the two samples which gave D=0.3 the sensitivity of VIII was 10 times higher than that of VII.

Example 4 Sample 1X which contained 0.001 parts by weight of hematein and the same amount of hematoxylin instead of 0.002 parts by weight of hematoxylin in Sample V1 of Example 2 per by weight of Zinc oxide was prepared. The characteristics of Sample V1 was in accord with that of Sample 1X within the 5 range of experimental errors and the deterioration was not caused by using hematein and hematoxylin in the same photosensitive layer.

The photosensitive layer becomes violet by addition of hematein and/or hematoxylin. The spectral sensitization of zinc oxide is made in accordance with this absorption spectrum. The principal feature of these additives, however, should be found in the ability to control average gamma of the characteristics curve. The ability spectral sensitization may be considered as a secondary matter.

prising zinc oxide, film formable resinous binder, sensitizing dye and at least one compound selected from hematein and hematoxylin, wherein said compound is incorporated therein in the range from 0.0001 to 2.0 parts by weight per parts of zinc oxide.

3. An electrophotographic photosensitive layer in accordance with claim 1 and which is used in the process of electrostatic electrophotography, wherein said compound is incorporated therein in the range from 0.0001 to 0.1 parts by weight per 100 parts of zinc oxide.

4. An electrophotographic photosensitive layer in accordance with claim 1, said compound is incorporated therein in the range from 0.0001 to 1.0 parts by weight per 100 parts of zinc oxide. 

2. An electrophotographic photosensitive layer comprising zinc oxide, film formable resinous binder, sensitizing dye and at least one compound selected from hematein and hematoxylin, wherein said compound is incorporated therein in the range from 0.0001 to 2.0 parts by weight per 100 parts of zinc oxide.
 3. An electrophotographic photosensitive layer in accordance with claim 1 and which is used in the process of electrostatic electrophotography, wherein said compound is incorporated therein in the range from 0.0001 to 0.1 parts by weight per 100 parts of zinc oxide.
 4. An electrophotographic photosensitive layer in accordance with claim 1, said compound is incorporated therein in the range from 0.0001 to 1.0 parts by weight per 100 parts of zinc oxide. 